What is a message queue?
Holds messages between programs: one adds them, another takes them off and does the work in its own time.
You upload a video, and the app says it's processing. It didn't make you wait. It put the job in line. That line is a message queue.
What it is
A message queue holds messages between programs. A producer adds them. A consumer takes them off and does the work, in its own time.
How it works
The upload service drops a message on the queue: this video needs processing. A pool of workers pulls messages off, one at a time. If a worker crashes mid-job, the message was never acknowledged, so it's delivered again. If a thousand uploads arrive at once, they just wait their turn. RabbitMQ and Amazon SQS are popular choices.
Why it matters
The app stays fast, one slow part can't drag down the rest, and when the line gets long, you just add more workers.
